What are AWS spot instances?

AWS spot instances are an excellent way to significantly reduce your EC2 on demand instance cost by up to 90%. Increasing numbers of companies, from SMBs to enterprises, have been leveraging spot instances for even mission-critical and production workloads. Spot instances pricing has helped them greatly optimize their cloud costs.

AWS spot instances represent AWS’s excess capacity. As a cloud provider, they must have spare capacity available for any surge in customer demand. To offset the loss of idle infrastructure, AWS offers this excess capacity at a massive discount to drive usage. That is why spot instances pricing is so affordable in comparison to EC2 pricing on demand.

When should you use Amazon spot instances?

The general perception of Amazon spot instances is that they are ideal for web services, containerized applications or other stateless, fault-tolerant workloads. 

However, in reality, they can also be used for a much broader set of use cases, without any significant impact on availability or performance. Here are some examples:

• Stateful applications typically require data and IP persistence. With automated solutions, even in the event of AWS spot instance replacement, your workload will immediately restart in the desired Availability Zone, from the same exact data point, maintaining root and data volumes as well as private and public IPs.
• Machine Learning is another area in which deep learning and training progress can be negatively impacted by unplanned AWS spot instance interruptions. But with the right tools, you can successfully run all your ML projects on spot instances. 
• CI/CD operations, whether Jenkins, Chef, Gitlab or others, can be run at scale on spot instances quite easily. 
• Big Data running on AWS EMR, Hadoop or Spark are great candidates for spot instances. 
• Distributed DBs such as Elasticsearch, Cassandra, Mongo which can handle a “reboot” of a single instance without losing data or affect service, can also run on spot instances.

What are Spot Instance Interruptions?

This discounted Amazon EC2 spot instance pricing comes with a caveat. AWS can “pull the plug” and terminate spot instances with just a 2 minute warning. These interruptions occur when AWS needs to draw from the excess capacity to service customers who purchased reserved instances, savings plans or on-demand instances. 

While AWS does offer “capacity rebalancing” signals which might notify you that an EC2 spot instance is at risk of termination, AWS does not guarantee these signals will be delivered early enough for you to take action.

Here are some of the reasons Amazon EC2 may interrupt a spot instance:

• Capacity—EC2 does not have enough unused instances to supply on-Demand or reserved instances, so it suspends spot instances to fulfill those requests.
• Constraint—if the spot instance request specified a launch group or Availability Zone group, and these constraints cannot be accommodated, instances will be terminated as a group.

When an instance is interrupted, you can select one of three possible actions—terminating the spot instance (default), stopping the spot instance (making it possible to restart it with the same launch specifications), or hibernating the instance.

How Can You Check and Select Pricing for Spot Instances?

You can find spot instance pricing on AWS’s spot instance pricing page as well as on the spot instance advisor page. This will help you determine the savings you can achieve in comparison to EC2 pricing on demand. 

Regarding the selection of your spot instance price, there is no real benefit to bidding higher than the default, on-demand price. 

This is true because:

• AWS determines the actual price based on overall market trends, not on specific, real-time bids
• AWS spot  instance interruptions are determined by AWS without any relation to your bid price 

Therefore, you can safely leave maximum price at whatever default AWS has it set to.

How Can You Check Spot Instance Price History?

If however, you only wish to spend a very specific amount, whether below the on-demand rate, or even below the current spot instance rate, you can check out historical spot instance prices, and specify your desired price. That way you will only run your EC2 spot instance when the actual market price matches your specific bid or is lower. 

To view spot price history:

1. Open the Amazon EC2 console and click Spot Requests. 
2. Select Pricing history.
3. Choose a product (operating system), instance type, and date range, and a price history is displayed. Move the pointer over the chart to see price trends over time.

Source: AWS

You can select from one of two pricing options for spot instances:

• Regular spot pricing—instances can be terminated with 2 minutes notice.
• Defined duration—you can get a spot instance guaranteed to run for a period of 1-6 hours. The longer the defined duration, the lower the discount provided for the spot instance. Defined duration instances grant discounts of 30-50% vs. On-Demand pricing.

What is AWS Spot Fleet?

Spot Fleet is a collection of spot instances. It makes it easier to respond to events on spot instances, such as instance termination, and provides central management, without requiring applications to continuously poll spot instances. 

You can create Spot Fleet requests using the Spot Fleet API or the CLI. A Spot Fleet request includes the number of instances required, type of instances, the target capacity, and maximum price.

EC2 tries to maintain the target capacity, adding spot instances if available, based on the request details. When spot instances are terminated, Spot Fleet attempts to replace them using the lowest price option available.

Automated Spot Instance Management with Spot by NetApp

While AWS Spot Fleet enables you to manage a large group or fleet of spot instances with different allocation strategies (i.e. lowest price, diversified, capacity optimized, etc.) along with many other options, to make it all work well, requires a large amount of manual configuration, setup and maintenance.

If you are looking for a turn-key solution to move more of your workloads to spot instances, with greater ease and confidence, here is a checklist of value-added functionality that you can get with Spot by NetApp.

To make AWS EC2 spot instances a real part of your cloud cost optimization strategy, see our Ocean product page for Kubernetes and containerized workloads and our Elastigroup product page for non-containerized applications.